The use of lighting elements, such as for example LED devices, is widely spread. One known problem of lighting elements is that they are often subject to aging effects. Aging effects refer to effects, such as for example a decrease in emission intensity, of lighting elements as function of the operation time. Furthermore, it is known that environmental conditions also can influence the performance of lighting elements, such as LED devices.
A plurality of techniques are known for compensating for aging effects. European patent application EP 2334144 describes a method of determining ageing characteristics of a LED whereby a current stress pulse is applied. The LED thereby is monitored to determine when the thermal heating induced by the current stress pulse has been dissipated to a desired level. The operational characteristics of the LED are then measured before applying a next stressing pulse. The technique presented typically is a test technique.
U.S. Pat. No. 5,859,658 describes an apparatus for compensating LED printbars for aging wherein changes in the slopes of the forward voltage drop versus forward current characteristics of the LEDs are determined and wherein the drive currents of the LEDs are changed as function of the changes in the slope so as to compensate for changes in the LED light output.
Nevertheless, there is still need for a good techniques for compensating for aging effects for LEDs.